In a well engineered network, signaling servers will not be overloaded under the normal operation mode. However, overload will occur if there are failures in the network or if there are significant increases in traffic load beyond the engineered loads. This can be the results of a disaster or mass calling due to a popular event such as reality TV shows, etc. In the former scenario, if the failures affect some signaling servers, the surviving servers will have to handle extra calls attempts. In the latter scenario, call attempts are generated so that call volumes are significantly higher than under normal operating mode.